Studies are proposed to examine the biology of the mycoplasma viruses and their possible role in human disease. Virus characterization will include electron microscopy and optical analysis of virus structure and biochemical properties of the viral proteins and nucleic acids. The growth parameters of Group 2 and 3 mycoplasma viruses will be studied. Transfection by these viruses will be examined, as compared with that by Group 1 viruses, and transfection of other types of cells will be investigated.